Wildlife Diseases

Avian Influenza  |  Sars-CoV-2 and Deer  |  Epizootic Hemorrhagic Disease in Deer  |  Sarcoptic Mange  |  Chronic Wasting Disease  |  Rabbit Hemorrhagic Disease  |  Rabies  |  Avian Influenza  |  West Nile Virus  |  Eastern Equine Encephalitis

PennVet's Wildlife Futures Program has created more than 50 fact sheets featuring diseases that affect wildlife of the Northeast U.S.

Sars-CoV-2 and White-tailed Deer

Recent research conducted by the United States Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) indicated that wild white-tailed deer were exposed to SARS-CoV-2, the virus that causes COVID-19 in humans. This research was not conducted in Connecticut, but positive results were found in several states, including New York and Pennsylvania. There is currently no evidence to indicate that deer can spread the virus to humans. The results are not surprising—deer are mammals that live in close proximity to humans—and other wild mammals have been shown to be susceptible to the virus that causes Covid-19. Additional research is underway. There also is no evidence the virus can be transmitted through food preparation and consumption. Hunters should always practice good hygiene while field dressing wild game. For tips on handling meat from wild animals, visit the CDC website.

Scientists still do not fully understand how wild deer were exposed to SARS-CoV-2 or how new variants may impact transmissibility among species. With this in mind, it is recommended that domestic animals are kept away from wildlife and wildlife carcasses as a precautionary measure. Direct and indirect transmission from people to wildlife is possible, thus reducing SARS-CoV-2 infection in the human population through preventive measures, including vaccination, is the best defense against human to deer transmission. (Note: Vaccination may not be recommended for immunocompromised people.)


Epizootic Hemorrhagic Disease in Deer

In October 2017, the first ever cases of Epizootic Hemorrhagic Disease (EHD) were confirmed in white-tailed deer in Connecticut. Symptoms of hemorrhagic disease in deer include swollen head, neck, tongue, or eyelids with a bloody discharge from the nasal cavity; erosion of the dental pad or ulcers on the tongue; and hemorrhaging of the heart and lungs, causing respiratory distress. The virus also creates high feverish conditions, causing infected deer to sometimes be found near water sources. EHD is transmitted by tiny biting flies (midges). All documented outbreaks tend to occur during late summer and early fall due to an increase in midge numbers and cease with the onset of a hard frost, which kills the midges carrying the virus.

No infected deer were reported in 2018 or 2019; however, in 2020 one deer tested positive for EHD in Ridgefield, with approximately 20 or more found in the surrounding areas near water bodies, indicating they may have died from EHD. New York experienced a heavy outbreak of EHD in 2021. Fortunately,  it was not found in Connecticut. In 2022, New York experienced an outbreak, as did Connecticut with more than 80 reports of deer suspected of dying from EHD and lab results confirming it in 4 of Connecticut's 13 deer management zones across the northwestern, south central, and southeastern portions of the state. Read the news release. In 2023, the Wildlife Division received a few reports of sickly-looking deer from concerned citizens. The deer were later tested, but there was no confirmation of EHD. The large amount of rainfall that occurred throughout the summer of 2023 was helpful in preventing another outbreak.

The DEEP encourages anyone who observes deer appearing emaciated, behaving strangely, or lying dead along the edge of waterbodies during summer to report the information, along with the closest address, to DEEP’s 24-hour Emergency Dispatch Center at 860-424-3333, the DEEP Wildlife Division at 860-418-5921, or send an email to Andrew.labonte@ct.gov.


Sarcoptic Mange

Coyote pup with sarcoptic mange.

One of the most prevalent parasitic diseases of red foxes and coyotes in Connecticut is sarcoptic mange. This disease is caused by a tiny mite that burrows beneath the skin of its host, causing the animal to scratch and rub intensely. Under certain conditions, infestations can cause death, especially when the animal’s discomfort prevents it from foraging and increases its vulnerability to predators.

Animals with mange have hair and weight loss; their skin is cracked and encrusted with heavy scabs. Secondary bacterial infections are common due to contamination by vigorous scratching.

DEEP does not capture and treat foxes and coyotes with mange. In this situation, it is best to let nature take its course, as difficult as that may be. Removal of mangy foxes and coyotes is challenging because many of these animals are still actively foraging and moving from place to place. However, some become severely weakened due to this illness and behave abnormally. If a sick or diseased coyote is seriously ill, laying down, struggling to move about, is acting abnormally or repeatedly found in yards posing an increased risk of contact with people and pets, it is recommended the animal be removed by local police or animal control officers. If local officials are unavailable, a DEEP Environmental Conservation Police Officer (860-424-3333) may be available to help.


Chronic Wasting Disease

What is Chronic Wasting Disease?
Chronic wasting disease (CWD) is a disease of the brain and nervous system in deer and elk that belongs to a family of diseases known as transmissible spongiform encephalopathies (TSE). This disease attacks the brains of deer, elk and moose and produces small lesions that eventually result in death. CWD is similar to another TSE disease, scrapie in sheep. No evidence exists that CWD affects humans or livestock.

Is CWD a new disease?
CWD was first recognized in captive mule deer in Colorado in the late 1960s, but was not identified as a TSE until the 1970s. CWD was first documented in wild elk in Colorado in 1981. Its discovery in wild deer in south-central Wisconsin in 2002 generated heightened attention from wildlife managers, hunters, and others interested in deer. CWD poses a significant threat to the deer and elk of North America and, if unchecked, could dramatically alter the future management of these species.

Captive deer infected with chronic wasting disease.

Captive deer infected with chronic wasting disease.

Why should we be concerned about CWD?
CWD is a relatively new disease and, consequently, there are a lot of unknowns. CWD does not cause an immediate widespread die-off of deer, but there may be long-term impacts to the herd if the disease is allowed to spread. Some scientists who have tried to predict the outcome on a deer population have described the disease as a 30 to 50-year epizootic with a potential to extirpate local populations. Others believe that the impacts might not be that severe. There are no proven solutions to eradicating the disease once present in wild populations. In addition, efforts by to contain or eradicate the disease can be extremely costly and labor intensive.

How does CWD spread?
The method of CWD transmission is unknown, however there is strong evidence to suggest that abnormally-shaped proteins called "prions" are responsible. The agent responsible for this disease may spread directly through animal to animal contact or indirectly through soil or other surface to animal contact. It is thought that the most common mode of transmission from an infected animal is via saliva and feces. A recent study confirms that CWD prions can be shed into the environment in feces from animals showing no clinical signs of the disease and can contaminate the soil, leading to infection in other animals. CWD can be spread from region to region by the movement of captive deer or through the improper disposal of a harvested deer transported from a CWD infected area.

Where has CWD been found?
Prior to 2005, the disease had only been found in North America west of Illinois. In 2005, CWD was documented in captive and free-ranging herds in New York and in free-ranging herds in West Virginia. Since then, it has also been discovered in several other states. CWD has not been found in Connecticut or New England. States and Canadian provinces where CWD has been confirmed include: New York, Pennsylvania, West Virginia, Virginia, Maryland, Tennessee, Missouri, Arkansas, Mississippi, Illinois, Iowa, Minnesota, Wisconsin, Michigan, Ohio, North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Texas, New Mexico, Colorado, Wyoming, Montana, Utah, Louisiana, North Carolina, Idaho, Alabama, Florida, Saskatchewan, Alberta, Manitoba, and Quebec. An updated map showing the states and Canadian provinces where CWD has been documented and what species have been affected can be found on the Chronic Wasting Disease Alliance website.

The first reported case of wild moose infected with CWD occurred in Colorado in September 2005. Because moose do not congregate like deer and elk, cases of CWD in moose are expected to remain low.

In April 2016, the first detection of CWD was found in Europe. The Norwegian Veterinary Institute diagnosed CWD in a free-ranging reindeer in South-Norway. This was not only the first detection of CWD in Europe but also the first detection of natural infection in reindeer worldwide. 

What is being done about CWD in Connecticut?
Connecticut and all other northeastern states have taken measures to prevent the spread of CWD. The Connecticut Department of Energy and Environmental Protection (DEEP) has taken the following CWD management actions:

  1. Connecticut, along with many other states, has banned the importation of live cervids (species in the deer/elk family) across state lines.
  2. An emergency regulation that was adopted in October 2005 to address concerns about CWD became permanent in September 2007. This regulation prohibits hunters from transporting into Connecticut any deer or elk carcasses or part thereof from any state where CWD has been documented, unless the meat has been de-boned. Specific wording of the regulation follows:
    • “Section 26-55-4: No person shall import or possess whole carcasses or parts thereof of any deer, moose, or elk from wild or captive herds from other states or Canadian Provinces where chronic wasting disease has been confirmed, including, but not limited to, Colorado, Wyoming, Utah, New Mexico, Montana, South Dakota, Kansas, Minnesota, Wisconsin, Illinois, Nebraska, Oklahoma, New York, West Virginia, Alberta and Saskatchewan. Any additional states* and provinces where chronic wasting disease is confirmed will be published in the Department's annual Hunting and Trapping Guide and on the Department's website. This provision shall not apply to meat that's de-boned, cleaned skullcaps, hides or taxidermy mounts.”
    • *See list above of additional states and Canadian provinces were CWD has been documented since this regulation was passed.
  3. In fall 2003, the DEEP, in cooperation with the UCONN Wildlife Conservation Research Center, initiated a surveillance program to determine if CWD existed in Connecticut. The program included testing deer using random surveillance of hunter-harvested and road-killed deer, and targeted surveillance of suspect animals (exhibited some symptoms consistent with CWD). Through random surveillance, over 230 samples were collected statewide and all tested negative for CWD. Deer were sampled from every county and deer management zone in the state. The extent of random sampling conducted in 2003 provides a high degree of confidence that CWD is not present in Connecticut. Through targeted surveillance, 4 suspect wild deer were collected and all tested negative for CWD (3 were hit by a vehicle and initially survived; 1 was an abandoned fawn being rehabilitated at a captive facility).
  4. In 2004, 298 randomly collected deer were tested for CWD from Deer Management Zone (DMZ) 11. Sampling efforts were focused in DMZ 11 because of the density of deer, relatively high number of captive deer facilities (6), and its close proximity to New York (New York has over 400 captive deer facilities with almost 10,000 deer and elk). Additionally, 6 suspect animals were collected and tested for CWD. All samples tested negative for CWD.
  5. From 2005-2011, a CWD surveillance program approved by USDA-APHIS was designed to focus sampling efforts in areas that were considered high and moderate risk. During this 7-year period, a total of 4,384 testable samples were collected from deer harvested during the archery, shotgun/rifle, or crop damage season and from deer found on roadways throughout the state.   
  6. Funding provided by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS) was eliminated from the federal budget in 2012, so no CWD testing was conducted in 2012 or 2013. However, a joint partnership between Connecticut DEEP and the Stewart B. McKinney National Wildlife Refuge, with financial assistance from the U.S. Fish and Wildlife Service, National Wildlife Refuge System (USFWS-NWRS), allowed for testing to be conducted in 2014 through 2016. With the testing of over 32,000 deer in New York with no additional CWD cases being documented, the DEEP Wildlife Division no longer considers deer management zones 1, 6, and 11 to be high risk. Therefore, sampling will be stratified across all zones based on deer density. Since 2014, about 350 samples were collected each year. Since sampling efforts began in 2003, no cases of CWD have been detected in Connecticut or New England. The Wildlife Division continues to collect samples to test for CWD. Hunters interested in donating deer heads for testing should keep the heads cool (not frozen) and arrange for them to be picked up by contacting Nathan Sajkowicz, Contractor for the Wildlife Management Institute at the CT DEEP Wildlife Division, at 860-418-5989

For the safety of Connecticut's deer herd, no person shall possess or use, for the purposes of taking or attempting to take or attract deer or for the surveillance or scouting of deer, any product bought or sold that is manufactured or refined that contains or purports to contain deer urine. Products labeled as "synthetic" may still be used. Products with vague descriptions about their contents are not recommended for use. CWD can spread through exposure to infected deer urine.

U.S. Fish and Wildlife Service logo*A presentation on chronic wasting disease has been developed, which is ideal for hunting and conservation clubs. If you would like a presenter to visit your club or organization, please email the U.S. Fish and Wildlife Service Stewart B. McKinney National Wildlife Refuge at Shaun_Roche@fws.gov, or call 860-399-2513.

*An informational rack card on CWD is available for printing and distribution.

How can I tell if a deer has CWD?
In early stages of infection, animals show no symptoms. The incubation period can range from about 1-5 years. In advanced stages, infected animals begin to display abnormal behavior, such as staggering or standing with very poor posture, and carrying the head and ears in a lowered position. In later stages of the disease, infected animals become emaciated. Some symptoms of CWD also may be characteristic of other diseases and conditions (e.g., bacterial brain abscesses and epizootic hemorrhagic disease, or deer that have been injured in a deer-vehicle accident).

What should I do if I see a deer that exhibits symptoms of CWD?
Do not attempt to handle, disturb, kill, or remove the animal. Accurately document the location of the animal and immediately contact the DEEP’s 24-hour hotline at 860-424-3333. Arrangements will be made to investigate the report.

How is CWD diagnosed?
Prior to 2008, the only method to definitively diagnose CWD was to examine the brain, tonsils, or lymph nodes in a laboratory. No live-animal test, vaccine, or treatment for CWD existed. In 2008, researchers from the USDA-APHIS and Colorado State University evaluated and validated the first live rectal-tissue biopsy method for detecting chronic wasting disease (CWD) in captive and wild elk. The live rectal biopsy test appears to be nearly as accurate as a post-mortem diagnostic test. The key advantage to the rectal biopsy test is that it can be performed on live animals. With this technique, managers can detect CWD in animals not showing any signs of the disease and, thus, remove them to decrease the likelihood of infecting other individuals. This new live test will improve management and control of the disease, especially in captive settings.

What precautions should Connecticut hunters take?
Concern over CWD should not limit hunter willingness to harvest deer during the hunting season. No evidence exists that CWD affects humans or that it exists in Connecticut. Even in states where CWD is found, nobody has ever contracted CWD. Studies have shown that the abnormal prions that cause CWD do not transmit to species other than members of the deer family. However, as a precaution, public health officials recommend that humans avoid consuming meat from deer suspected of being infected with CWD. The CWD prion can be found within the meat of deer in the terminal stages of CWD. Higher levels of infected prions accumulate in tissues, such as the brain, spinal cord, spleen, lymph nodes, tonsils, and eyes, and as a precaution, contact with these items should be minimized.

Hunters should exercise the following precautions.

  • The use of natural urine-based lures is prohibited by state regulation.      
  • Avoid shooting, handling, or consuming any animal that is behaving abnormally or appears to be sick. 
  • Wear latex or rubber gloves when field dressing deer. 
  • Minimize the handling of and do not eat the brain, spinal cord, eyes, spleen, tonsils, and lymph nodes. 
  • De-bone meat from the animal. Do not saw through bone or cut through the brain or spinal cord (backbone). 
  • Wash hands and instruments thoroughly after field dressing is completed. Instruments should be placed in a 1:1 bleach/water solution for an hour and left to air dry before reusing. 
  • If you plan to hunt for deer or elk in another state, contact the state’s wildlife agency for the latest information on CWD and restrictions on transportation of harvested animals. 
  • To avoid possible introduction of high risk tissues from CWD-infected animals harvested outside of Connecticut, hunters should return with only boned-out meat, antlers with cleaned skull caps, hides without the head, and finished taxidermy mounts. This is mandatory if the deer was taken from a state known to have CWD. 
  • Dispose of carcasses by burying them or bringing them to landfills which accept carcasses. 
  • Carcasses from animals harvested in CWD-infected states and disposed of in the woodlands of Connecticut could result in an outbreak of CWD in our state.

The New York Department of Environmental Conservation adopted a rule change in 2019 that prohibits hunters from entering New York with whole carcasses or intact heads of deer, elk, moose, or caribou that they harvest anywhere outside of New York. Review the NYDEC's Big Game Importation Restrictions for more information.

Can I have my deer tested for CWD?
The Deer Program at Franklin Wildlife Management Area will be testing some deer as part of its annual surveillance for CWD. State testing typically occurs from mid-September through the end of January. If you would like to have your deer tested free-of-charge during the collection period, call Nathan Sajkowicz, Contractor for the Wildlife Management Institute at the CT DEEP Wildlife Division, at 860-418-5989. Prior to testing, the deer's head should be kept cool but not frozen.

How can I find out more about CWD?
Persons wanting more information on CWD are advised to visit the following web sites:

Some of the above information was taken from CWD publications produced by other private organizations and state agencies.

Rabbit Hemorrhagic Disease

New England cottontail rabbit in the brush.

Rabbit hemorrhagic disease is a fatal disease in rabbits and is considered a foreign animal disease in the United States. This disease is caused by several virus strains. Animal health officials detected one of these strains, Rabbit Hemorrhagic Disease Virus Serotype 2 or RHDV2, in North America in the past few years. RHDV2 is highly contagious and, unlike other rabbit hemorrhagic disease viruses, it affects both domestic and wild rabbits, including hares, jackrabbits, and cottontails. The New England cottontail (pictured), eastern cottontail, and snowshoe hare, which are found in Connecticut, are susceptible to infection and mortality. At this time, RHDV2 is not known to impact humans or other animals.

As of September 2022, RHDV2 has been confirmed in 27 states (including Connecticut) with cases involving domestic, feral, and wild rabbits and hares. On September 11, 2022, a number of cases isolated to one location in Hartford County in Connecticut were confirmed in domestic rabbits. Natural resource agencies have reported events in which three to more than 1,000 rabbits and hares have died. The outbreak in the southwestern U.S. is linked to a different strain than the outbreak in the Pacific Northwest and New York, suggesting at least two separate introductions of the virus. RHDV2 has also infected pet rabbits and feral rabbits (domestic rabbits that have been released or escaped from captivity and now live in the wild).


The RHDV2 virus is very resistant to extreme temperatures, and can stay viable for months. Rabbits can get the virus from contaminated food and water, contact with infected rabbits, and contact with feces of predators or scavengers that have eaten infected rabbits. People can spread the virus indirectly by carrying it on their clothing and shoes. The first sign of infection is often the sudden and unexpected death of a previously healthy rabbit.

People can inadvertently spread RHDV2 into the wild by releasing domestic or unwanted pet rabbits or through improper disposal of dead rabbits.

Symptoms of RHDV2

Many times, the only signs of the disease are sudden death and blood-stained noses caused by internal bleeding. Infected rabbits may also develop a fever, be hesitant to eat, or show respiratory or nervous system signs, such as poor balance or involuntary movements.

Is RHDV2 a Conservation Concern?

Scientists believe that all rabbits and hares are susceptible, including the eastern cottontail, snowshoe hare, and our only native rabbit, the New England cottontail.

While RHDV2 has not been confirmed in wild rabbits in eastern North America, biologists and other experts are very concerned. The disease spreads quickly and easily in the wild and could easily wipe out species with small populations, such as the New England cottontail.

Rabbits play an important role in our ecosystem. They help control herbaceous vegetation and are an important part of the food chain for many predators, such as bobcats.

What Is the Wildlife Division Doing to Safeguard New England Cottontails?

The New England cottontail is found in parts of Maine, New Hampshire, Massachusetts, Connecticut, Rhode Island, and New York east of the Hudson River. An estimated 13,000 of these secretive animals exist today. The species’ population has decreased dramatically because its young forest and shrubland habitat is declining. Cooperative efforts between the Connecticut Wildlife Division, U.S. Fish and Wildlife Service, Natural Resources Conservation Service (NRCS), Wildlife Management Institute, other state wildlife agencies, and non-governmental organizations have resulted in habitat restoration, outreach and education, and monitoring and assessment of New England cottontail populations. To help stabilize declining populations and initiate recovery, state fish and wildlife agencies, private landowners, and other conservation partners have worked hard to enhance and protect thousands of acres of young forest and shrubland habitat critical to this rabbit’s survival. When animals have abundant habitat that supplies ample food and hiding cover, they will be healthier and less susceptible to diseases.

The Wildlife Division has been working closely with the U.S. Department of Agriculture and the State Veterinarian’s office to develop monitoring and testing protocols and increase awareness about this very serious disease. The Division is also working closely with other states across the country to monitor the spread of the disease and develop ways to prevent it from impacting new areas.

How Can You Protect Wild Rabbits?
  • The Connecticut State Veterinarian announced in November 2021 that an experimental vaccine for Rabbit Hemorrhagic Disease Virus has been approved for use by Connecticut licensed veterinarians. Those who own domestic rabbits may want to consider getting their rabbits vaccinated.
  • Never release domestic or pet rabbits or hares into the wild since they may spread RHDV2, even if they seem healthy. In their early stages, many diseases, including RHDV2, are difficult or impossible to detect visually. (Released pets may also compete with rabbits, hares, and other animals by using food and other resources that wildlife depend on.)
  • If you own a domestic rabbit and it becomes ill or dies suddenly, contact your veterinarian or the Connecticut Department of Agriculture’s State Veterinarian. After handling such a rabbit, wash your clothes in hot water and detergent and disinfect all contact surfaces.
  • Hunters and trappers should avoid taking rabbits that appear sick. Wear disposable gloves when handling game, double-bag carcasses and other remains and put them in the trash, and thoroughly clean knives and other equipment. Harvested rabbits should be cooked to a temperature of 165 degrees Fahrenheit. Further information is available for: Hunters, Hound Hunters, and Falconers.
  • If you see a healthy rabbit suddenly die or find several dead rabbits in the same area, contact the DEEP Wildlife Division at 860-424-3011 or deep.wildlife@ct.gov.
Additional Resources on RHDV2

September 2022 CT Dept. of Agriculture RHDV2 Press Release

Working Together for the New England Cottontail (NewEnglandCottontail.org)

RHDV2 Fact Sheet from the PennVet Wildlife Futures Program

RHDV2 Fact Sheet from the U.S. Department of Agriculture

RHDV2.org from the RHDV2 Awareness Team at the University of Georgia

Content last updated in November 2023.